Doctoral Dissertation Research: Role of Transportation in Employment Outcomes of the Disadvantaged

负担得起的高效交通对低收入个人的就业至关重要，因为他们用于流动的资源较少。为了帮助改善弱势群体的就业结果，规划者和政策制定者强调了交通的重要性，并建议扩大公共交通服务或以更低的成本提供汽车。为了证明这些政策努力的合理性，许多研究人员研究了交通运输对弱势群体劳动力市场结果的影响。这些研究集中在一个关键因素上--处于不利地位的个人是否有足够的“可获得性”来获得就业机会。因此，有一个基本假设，即可获得性和就业是相互直接联系的。也就是说，过去的研究建立在这样的观点之上，即获得可靠交通选择或更容易获得就业机会的低收入个人将为工作出行选择特定的交通方式。尽管这看似合乎逻辑的假设，但仅凭可访问性并不能保证个人选择某种旅行方式。通过系统地考察低收入人群的出行方式选择决策，本论文的目的是揭示当前人们对经济弱势群体可及性与就业之间关系的认识。特别是，这个项目提出了两个研究问题。首先，决定低收入人群出行方式选择的因素有哪些？其次，在系统考虑出行方式选择后，就业可及性是否仍对改善贫困人群的就业结果具有直接和独立的影响？这项研究使用在旧金山和亚特兰大地区收集的家庭旅行调查数据，通过进行一系列统计分析来估计穷人的就业结果，以此作为可获得性和旅行方式选择的函数，从而解决上述问题。研究人员希望证明模式选择决策在考察可获得性对低收入个人就业结果的影响方面的重要性。本论文在两个方面具有重要意义。首先，很少有研究系统地将穷人的出行方式选择纳入研究可达性对就业的影响；很少考虑到交通工具提供的高水平工作可及性并不能保证个人会选择特定的出行方式。因此，文献中缺少的是可达性如何影响穷人的出行方式选择，以及出行方式决定随后如何影响就业。拟议的研究将填补文献中的这一空白。其次，本研究的发现将为未来的交通政策提供指导。目前针对穷人的交通政策往往侧重于通过提供汽车或扩大交通服务来提高可达性。然而，如果这项研究发现有特定于每个人的因素限制了他们的出行方式选择，如果方式选择确实对就业有重大影响，这项研究可以向政策制定者告知限制可获得性价值的这些限制因素的来源。然后，公共部门可以设计专门旨在消除这些制约因素的政策工具，从而确保从目前的增进无障碍战略中获得更高的社会回报。

Affordable and efficient transportation is crucial for the employment of low-income individuals, as they have fewer resources to spend on mobility. To help improve employment outcomes of the disadvantaged, planners and policy makers have emphasized the significance of transportation and suggested expanding public transit services or providing automobiles at lower cost. To justify such policy efforts, numerous researchers have studied the impact of transportation on labor market outcomes of the disadvantaged. The studies have focused on a key element -- whether or not disadvantaged individuals have adequate "accessibility" to reach job opportunities. Thus, there is a fundamental assumption that accessibility and employment are directly connected to each other. That is, the past research is built upon the idea that low-income individuals with reliable access to a transport option or higher accessibility to job opportunities by car or public transit will choose a particular transport mode for work-related travels. Despite this seemingly logical assumption, accessibility alone does not warrant an individual's choice of a certain travel mode. By systematically considering travel mode choice decisions of low-income individuals, the objective of this dissertation is to shed new light on the current understanding of the relationship between accessibility and employment of the economically disadvantaged. In particular, this project asks two research questions. First, what are the factors determining travel mode choices of low-income individuals? Second, after systematically considering travel mode choices, does accessibility to jobs still have a direct and independent impact on improving employment outcomes of the deprived? This research, using household travel survey data collected in the San Francisco and Atlanta regions, addresses the above questions by conducting a series of statistical analyses to estimate employment outcomes of the poor as a function of accessibility and travel mode choices. The investigators expect to demonstrate the significance of mode choice decisions in examining the impact of accessibility on the employment outcomes of low-income individuals. This dissertation is important in two respects. First, few research studies have systematically integrated travel mode choices of the poor in studying how accessibility affects employment; little consideration has been given to the idea that a high level of job accessibility provided by a transport means does not guarantee that individuals will choose the particular travel mode. Thus, what is missing in the literature is how accessibility affects travel mode choices for poor individuals, and how travel mode decisions subsequently influence employment. The proposed study will fill this gap in the literature. Second, the findings from this research will offer guidance for future transportation policy. Current transportation policies for the poor tend to focus on improving accessibility by providing cars or expanding transit services. However, if this study finds that there are factors specific to each individual that restrict their travel mode choices, and if mode choices indeed have significant impact on employment, this research can inform policy makers about the sources of such constraints that limit the value of accessibility. The public sector can then design policy instruments that are specifically aimed at removing such constraints, thus ensuring higher social returns from present accessibility-enhancing strategies.